To collect sensor information as an input for control in a control apparatus within a vehicle, sometimes a plurality of data are required to be collected at the same time and compared with each other.
In a power feeding circuit installed on the vehicle, sometimes, for example, a conductive portion of wire is exposed and keeps contact with a grounding so as to produce a complete short-circuit or chattering that the conductive portion makes contact with the grounding intermittently and cyclically due to vibration or the like during traveling of the vehicle occurs. In these cases, leakage of electricity occurs in the power feeding circuit.
As a method for detecting for leakage of electricity on this power feeding circuit, there is available a method for detecting whether or not leakage of electricity Id is present by detecting currents I1, I2 at two potentials using current sensors 5, 7 when feeding power from a vehicle installed power supply 1 containing a battery to a load 3 and comparing a difference ΔI (I=I1−I2) with a comparison circuit 9. According to such a method, if that difference ΔI is over a specified level, after it is determined that the leakage of electricity Id is caused in a current passage L1 between both the current sensors 5 and 7, an output signal from the comparison circuit 9 is amplified by an amplifier 11 and a circuit breaker 13 is operated corresponding to a signal from this amplifier 11 so as to interrupt supply of electricity from the vehicle installed power supply 1 to the load 3.
In an assembled battery for use in a vehicle, sometimes, a current value of each of individual batteries which constitute this assembled battery and the total current value of the entire assembled battery is obtained so as to control the load of the vehicle based on these current values.    Patent document 1: Japanese Patent Application Laid-Open No. 2001-037068
In the above-described patent document 1, the currents I1, I2 at two locations are detected using a pair of the current sensors 5, 7 and its detection results are compared with the comparison circuit 9. Conventionally, the detection results of the respective current sensors 5, 7 are converted to voltage values and the voltage values are transmitted to the comparison circuit 9 through wires 15, 17.
Consequently, the quantity of the wires 15, 17 increases so that not only the assembly step becomes complicated but also this is inconsistent with a demand for reduction of wires in the vehicle. Particularly, in vehicle field in which advanced control is demanded using sensor information in near future, the weight of the wires affects vehicle performance badly.
If resistance values of the pair of the wires 15, 17 are different, the voltage values outputted from the current sensors 5, 7 drop by the time when they are supplied to the comparison circuit 9 through the wires 15, 17, so that the currents I1, I2 cannot be grasped accurately by the comparison circuit 9.
Such a problem is common to other application example of collecting both the total current values of the assembled battery and the current value of each of individual batteries which constitute the assembled battery.
In views of such a problem, it can be considered to construct a network within the vehicle using specialized hardware having communication function as a solution. Consequently, bad influences due to a difference between the resistance values of plural wires can be eliminated by digitizing the signals, as well as the reduction in weight and the simplification of the manufacturing step by reducing the quantity of the wires.
Here, existing communication system in control network field is largely classified to event driven type and regular transmission type. In order to collect data synchronously in any type, a specified signal is transmitted by broadcasting and when that signal is received, data is collected and then, the data is transmitted to a data requester in other chance.
However, if such operation (broadcasting) is achieved on upper layer of communication layer, time lag due to operation of software installed with upper layer becomes likely to occur, so that data collection is not carried out at the same time. For example, in the event driven type, if completion of collection of response data is intended to be achieved with hardware after the data collection request signal is transmitted, the circuit becomes complicated. Thus, as an existing communication system in the field of the control network, system containing software is achieved.
In addition to the simultaneity, if the frequency of data collection is increased, a high-speed CPU needs to be used, so that the load on the CPU increases, which is a problem to be solved.
In the network in the vehicle, for example, plural networks are connected through gateway and mutual communication is carried out through this gateway. Because the time lag unavoidably occurs when data is exchanged through the gateway in this case, when it is intended to collect sensor information on the plural networks exceeding a single network synchronously, a cycle start signal timing alone is insufficient and additionally, the time lag of the cycle start signal timing between the networks needs to be solved.